Vascular smooth muscle cell apoptosis in abdominal aortic aneurysms.

Apoptosis is a naturally occurring mechanism of cell death that plays an important role in both normal and pathological remodeling of the vessel wall. Abdominal aortic aneurysms (AAA) represent a unique and dramatic example of vessel wall remodeling characterized by degeneration of the elastic media. Although much attention has been focused on the proteolytic mechanisms that underlie elastin and collagen degradation in AAA, recent studies suggest that depletion of medial smooth muscle cells (SMC) makes an important contribution to this disease by eliminating a cell population capable of directing connective tissue repair. As described in this review, these investigations have revealed that SMC depletion in human aneurysm tissues is accompanied by biochemical, morphological and molecular changes consistent with SMC apoptosis. The exact mechanisms responsible for SMC apoptosis in AAA remain to be elucidated, but current evidence indicates that elevated cellular production of p53 and p21 participates in the process. These findings provide an important new starting point for further investigations on the cellular and molecular mechanisms underlying SMC depletion in AAA and how this process might trigger the accelerated progression of aneurysm disease.